[PATCH proxmox-backup v4 15/22] datastore: refactor shared request counter loading into helper

[Christian Ebner <c.ebner@proxmox.com>]

In preparation for also setting/updating the threshold values and
notification callback.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-datastore/src/datastore.rs | 84 +++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 38 deletions(-)

diff --git a/pbs-datastore/src/datastore.rs b/pbs-datastore/src/datastore.rs
index 0ae2f7b59..dac92ce3d 100644
--- a/pbs-datastore/src/datastore.rs
+++ b/pbs-datastore/src/datastore.rs
@@ -684,49 +684,34 @@ impl DataStore {
                 .parse_property_string(config.backend.as_deref().unwrap_or(""))?,
         )?;
 
-        let (lru_store_caching, request_counters) = if DatastoreBackendType::S3
-            == backend_config.ty.unwrap_or_default()
-        {
-            let mut cache_capacity = 0;
-            if let Ok(fs_info) = proxmox_sys::fs::fs_info(&chunk_store.base_path()) {
-                cache_capacity = fs_info.available / (16 * 1024 * 1024);
-            }
-            if let Some(max_cache_size) = backend_config.max_cache_size {
+        let (lru_store_caching, request_counters) =
+            if DatastoreBackendType::S3 == backend_config.ty.unwrap_or_default() {
+                let mut cache_capacity = 0;
+                if let Ok(fs_info) = proxmox_sys::fs::fs_info(&chunk_store.base_path()) {
+                    cache_capacity = fs_info.available / (16 * 1024 * 1024);
+                }
+                if let Some(max_cache_size) = backend_config.max_cache_size {
+                    info!(
+                        "Got requested max cache size {max_cache_size} for store {}",
+                        config.name
+                    );
+                    let max_cache_capacity = max_cache_size.as_u64() / (16 * 1024 * 1024);
+                    cache_capacity = cache_capacity.min(max_cache_capacity);
+                }
+                let cache_capacity = usize::try_from(cache_capacity).unwrap_or_default();
+
                 info!(
-                    "Got requested max cache size {max_cache_size} for store {}",
+                    "Using datastore cache with capacity {cache_capacity} for store {}",
                     config.name
                 );
-                let max_cache_capacity = max_cache_size.as_u64() / (16 * 1024 * 1024);
-                cache_capacity = cache_capacity.min(max_cache_capacity);
-            }
-            let cache_capacity = usize::try_from(cache_capacity).unwrap_or_default();
 
-            info!(
-                "Using datastore cache with capacity {cache_capacity} for store {}",
-                config.name
-            );
+                let cache = LocalDatastoreLruCache::new(cache_capacity, chunk_store.clone());
+                let request_counters = Self::request_counters(&config, &backend_config)?;
 
-            let cache = LocalDatastoreLruCache::new(cache_capacity, chunk_store.clone());
-
-            let path = format!(
-                "{}/{}-{}-{}.shmem",
-                S3_CLIENT_REQUEST_COUNTER_BASE_PATH,
-                backend_config
-                    .client
-                    .as_ref()
-                    .ok_or(format_err!("missing s3 endpoint id"))?,
-                backend_config
-                    .bucket
-                    .as_ref()
-                    .ok_or(format_err!("missing s3 bucket"))?,
-                config.name,
-            );
-            let request_counters =
-                SharedRequestCounters::open_shared_memory_mapped(path, pbs_config::backup_user()?)?;
-            (Some(cache), Some(Arc::new(request_counters)))
-        } else {
-            (None, None)
-        };
+                (Some(cache), Some(Arc::new(request_counters)))
+            } else {
+                (None, None)
+            };
 
         let thread_settings = DatastoreThreadSettings::new(
             tuning.default_verification_workers,
@@ -748,6 +733,29 @@ impl DataStore {
         })
     }
 
+    /// Load the shared s3 request counters for given datastore and backend config
+    pub fn request_counters(
+        config: &DataStoreConfig,
+        backend_config: &DatastoreBackendConfig,
+    ) -> Result<SharedRequestCounters, Error> {
+        let path = format!(
+            "{}/{}-{}-{}.shmem",
+            S3_CLIENT_REQUEST_COUNTER_BASE_PATH,
+            backend_config
+                .client
+                .as_ref()
+                .ok_or(format_err!("missing s3 endpoint id"))?,
+            backend_config
+                .bucket
+                .as_ref()
+                .ok_or(format_err!("missing s3 bucket"))?,
+            config.name,
+        );
+        let request_counters =
+            SharedRequestCounters::open_shared_memory_mapped(path, pbs_config::backup_user()?)?;
+        Ok(request_counters)
+    }
+
     // Requires obtaining a shared chunk store lock beforehand
     pub fn create_fixed_writer<P: AsRef<Path>>(
         &self,
-- 
2.47.3